The ionic concentration of a solution can be determined using, for example, spectroscopy, chromatography, calorimetry, optical fluorescence, or a potentiometric titration. These techniques require large laboratory equipment, and are therefore not portable. Indeed, most hospital electrolyte tests are performed in large, multiple-analyte analyzers in a chemistry or medical laboratory. Vials of blood are drawn from the patient for sampling, and hours, and even days, may pass before the caregiver receives the results.
Recently, however, ion-selective electrode technology has made point-of-care (POC) electrolyte testing feasible. For example, the i-STAT system, available from the i-STAT Corporation, utilizes a blood sample that is drawn from the patient and injected into a cartridge including micro-fabricated, ion-selective electrodes, a calibration fluid pouch, and plastic structures for directing fluid flow and storing waste. The fluid pouch, containing known concentrations of the analytes, is punctured at the onset of a test, and the calibration fluid passes over the sensors, allowing a one-point calibration. The fluid is then flushed into the waste container and the blood sample is drawn in for testing. The cartridges are disposable, but are only good for a single use.
While i-STAT's cartridge system represents an improvement to existing POC testing, less-invasive medical diagnostics that incorporate re-usable components, and therefore produce less medical waste and are less-expensive, would be desirable.